Infrared transmitting glasses



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INVENTOR-S GIVE/V W. GLEEK EDGAR H. HAMILTON ATTORNEYS Feb. 20, 1962 G.w. CLEEK ETIAL 3,022,182

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United States Patent "ice 3,022,182 INFRARED 'IRANSMI'ITING GLASSESGiven W. Cleek, Arlington, Va., and Edgar H. Hamilton, Silver Spring,Md., assignors to the United States of America as represented by theSecretary of the Navy Filed July 17, 1956, Ser. No. 598,482 2 Claims.(Cl. 10652) (Granted under Title 35, US. Code (1952), sec. 266) Theinvention described herein may be manufactured and used by or for theGovernment of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

This invention relates to glass compositions and more particularly toinfrared transmitting glass compositions based on the BaOTiO -SiOternary system.

Application of infrared transmitting glasses in the field of optics hasbecome more prevalent and diversified due largely to the demandspresented by military usages, such as in optical lenses for aerialphotography equipment and fire control instruments. stringentrequirements of physical and chemical properties for infraredtransmitting glasses have been made necessary due to the wide range ofenvironmental factors surrounding practical applications of the deviceswhich employ these glasses.

Research directed toward the development of serviceable glasses based onternary systems, such as K O- CaO-Si0 and K OPbOSiO has led to thediscovery of commercial glasses which are fluid enough at anindustrially accessible temperature to be melted on a commercial scale,viscous enough to be worked above its freezing point so thatdevitrification cannot take place, and glasses which have physicalproperties and chemical durability suitable for the purpose for whichthey are intended. However, studies made to lead to the production ofspecial-type glasses capable of resisting cheinical and physical changeordinarily brought about through exposure to extremes of heat and coldand corrosive chemicals have resulted in the finding of relatively fewAn object of the present invention is to provide infrared glasses ofhigh refractive index.

Another object of the invention is the provision of infraredtransmitting glasses having high deformation temperatures.

Another object is to provide glasses having good chemical durabilitiessuch as resistance to attack over the entire pH range and lowhygroscopicity.

A further object is to provide infrared glasses of a composition whichenables the glass to be cooled from a molten state withoutcrystallization.

A still further object of the invention is the provision of a glasshaving good transmittances in the near infrared at wave lengths belowfive microns.

Another object is to provide glass compositions based on the BaOTiO 4iGternary system which may be formed in relatively large amount melts.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

30 ponent glasses of the invention which have SiO --50, BaO--30, TiO-20, respectively.

3,022,182 Patented Feb. 20, 1962 FIG. 1 is a graph illustratingrefractive index N versus Nu value of various crown and flint glasses incomparison with the BaO-TiO SiO- type glasses of the present invention;

FIG. 2 shows the transmittance property curves for 2 mm. thicknesses ofrepresentative glasses of the invention;

PEG. 3 illustrates a thermal expansion curve of one member of theglasses comprising the invention;

FIG. 4 is a graph showing the Nu values and refractive index, N of theLa O series of the base glass F138;

H68. 5 and 6 illustrate the transmittance curves of 2 mm. thicknesses ofglasses in one series of glasses of the invention;

PEG. 7 shows the transmittance curves for 2 mm. thicknesses of threeglasses in the 210 series of the invention; FIG. 8 illustratestransmittance curves for 2 mm. thicknesses of two glasses in the ThOseries of the invention;

FIGS. 9 and 10 show transmittance curves for 2 mm.

thicknesses of glasses based on the Ta O and-Th0; series glasses of theinvention;

FlG. 11 illustrates transmittance curves for a 2 mm.

FIG. 12 illustrates transmittance curves for 2 mm and 8 mm. thicknessesof glass F161 of the invention;

, FIGS. 13 and 14 are the thermal expansion curves for two glassesdeveloped from the ternary base glasses; and,

FIG. 15 is a plot of elastic moduli for two multicombeen de' velopedfrom the ternary base glasses.

According to the present invention it has beenfound;

that multicomponent glasses having desirable characteristic propertiesmay be developed from the ternary base glasses of the BaOTiO SiO system.:Not only has it been discovered that glasses comprising the presentinvention are feasible in their intended use in optical lens devicesrequiring infrared Wave transmission, but also that the glasses may beprepared in large melts which factor contributes tomass production ofthe glasses in microns, high deformation temperatures, and good chemicaldurabilities. A considerable glass forming range has been accomplishedin the ternary BaOTiO -SiO system, and it has been discovered that therefractive indices,

N of these glasses range from 1.631 to 1.880 with Nu values from 49.9 to25.3. Further, considerable variation in transmittance has been noticedfor the several glasses, but in general the glasses containing 15, 20,and 25 mole percent TiO show the best transmittance in the region 5 of3.5 to 4.0 microns, the absorption band near 3.0 microns being theweakest for these glasses. Particular examples of glasses formed whichincludes the favorable properties above-noted are F138 and F40 eachconsisting of, in mole percent, SiO -40, Ba0 30, TiO -30; and

glasses have the property of high refractive index, F-138,

N of 1.83697, and F40, N of 1.75412, with Nu values of 28.1 for F-l38and 34.3 for F 40.

These 7 type of antiref'lection coating applied in alkaline solutioncannot be used on glasses with high PbO contents, since the resistanceto attack by alkaline solutions is poor. In contradistinction, theglasses provided by this invention 5 have a high chemical stabilityinasmuch as the PbO content is low, and yet the resultant glasses.compare favorably to the physical properties of the extra dense flintglasses.

d by the.

C. is well above It readily After viewed f monochromatic the exposedportion e amount of attack The transmittance propthe interference bandsF 64, F62, F65,

. 3. It is important to note that was immersed about one half C. thesamples were for 2 mm. thicknesses of the glasses.

the thermal expansion curve for reciated that a considerable glassforming range g media, a measure of chemical durability Glasses of thisnature have little or no trans- Inasmuch as any shifts in It is alsonotable that known high refractive index oxide. mittance beyond Wavelengths of 2.9 microns whereas glasses described herein contain no 13and the transmittances extend beyond wave lengths of 2.9 microns,

5 thus making the glasses of this invention suitable for infraredtransmittance purposes. erties of several glasses typical of the presentinvention are plotted in FIG. 2

The deformation temperatures, as determine thermal expansion method, ofexemplary glasses of the invention generally range from 767 C. to 840.C. For

purposes of illustration,

glass F125 is given in FIG the deformation temperature of 827 index, andis well above the deformation temperatures of most commercial types ofglass.

Transmittances of the base glasses of Table I on which are formed oxideseries are shown in FIG. 2. can be app is covered in the ternary BaOTiOSiO system by reference to FIG. 2, as mentioned above.

The chemical durabilities of the glasses above-note were determined byan interferometric method. A polished sample of each glass its length ina solution buffered to the desired pH. six hours exposure at 80 throu han optical flat with the aid 0 ht. as they passed from the unexposed toof the sample were proportional to t by the bufterin of the sample wasaccurately determined. The results SiO type glasses are given in thefollowing Table II. It is noteworthy that seven glasses, F48,

F158, F161,.F223, F232, all of which contain either Ta O or ZrO or both,show no detectable attack overglasses usually contain appreciableamounts of boron g-g that of extra dense flint glass of comparablerefractive 0-4 7 of tests on the samples noted in Table I of BaOTiOTable 1, below, It is upon the lained more in iuonao Div-azoosn mooooo dtransmittance and f the resulting glasses.

f glasses have been en that'representaking, extra dense esence ofmoderate to des, particularly Na O frare TABLE I Base glasses forvarious oxide series [Percent] -listed oxides within their given ofOxide substitutioXL LazOa RUSOOOOG UAUOQdOQOQuOOOOO 'F40 F123 F F154F158 F138 F201 F216 F220 F223 The following is a table showing thetransmittances of some glasses of the invention: Transmittances of baseglasses for each series of oxides .IODS

More broadly, representative glasses of the invention 'may be formed ofthe following oxides within the quantitative mole percentage rangeslisted.

It has been revealed by this invention that small amounts of otheroxides, such as Na O, K 0, CaO, Sr0, ZnO, CdO, TeO and A1 0 also may beincluded as Specific glasses of the ternary system BaO-TiO --SiO SiO35-60 Th0 BaO 15-35 ZrO glass components, although the pr large amountsof some of these oxi and K 0, materially impair the in lower thedeformation temperature 0 mole percentage ranges are represented in andare expressed in molefpercentage.

glasses of Table I that oxide series 0 discovered, and these series willbe exp detail hereinafter.

By referring to FIG. 1, it can be se tive glasses of the invention-haverefractive indices comand Nu values somewhat As is well-known in the artof glass ma are not chemically durable. For example, one '75 the entirepH range from pH 2 to pH 12.

parable to the extra dense flints higher.

flint glasses have PbO as a major constituent, and, consequ y TABLE HHygroscopicity and chemical durability of BaO-TiO SiO glasses Watersorbed Surface alteration, fringes, at pH (exposures,

6111'. at 80 C.) Melt No.

1 hr. 2 hr. 2.0 4.1 6.0 8.2 10.2 11.8 mgJcm. rug/cm.

5.7 10.0 ND ND ND ND 0.511 2A 6.1 9. 1 ND ND ND ND ND 2A 5. 2 8.2 0. 1AND ND ND ND ND 3. 8. 0 3 0. 18 ND ND ND ND ND 6. 2 7. 9 ND ND ND ND NDND 4. 0 7. 2 ND ND ND ND ND ND 5. 3 8.1 ND ND ND N'D ND ND 4.7 8.1 ND NDND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 5. 5 13. 5 ND ND ND NDND ND 5. 0 11.0 ND ND ND ND ND ND Fused S102. 6.2 12.1 ND ND ND ND 4 DA0. 5A Corning 7740 15. 9 28. 3 ND ND ND DA 0. A 1. 75A

1 ND, no detectable attack.

I A, attack of surface.

3 S, swelling of surface.

4 DA, detectable but not measurable attack.

Hubbard, Donald, J. Res. NBS, 36, 36509460111 1706.

The hygroscopicity, or tendency of a powdered glass 11. The valuesobtained are, in all cases with the exception of F223 in the 2 hr.column, equal to or lower than fused SiO which was used for purposes ofcomparison.

Hygroscopicity of Optical Glasses an as Indicator of Serviceability,

The resistance of these glasses to chemical attack over sample to absorbwater, is also shown in the above Table the entire pH range and theirlow hygroscopicity make them unique as compared to commercial types ofglass.

Variations of the ternary base glasses F40 and F138 having desirablecharacte Tables III and IV.

TABLE III [Compositions in mole percent] ristics are given in thefollowing F145 F146 F147 F148 F149 F150 F151 40 45 50 55 6O 65 7O 25 2525 25 25 25 25 30 25 20 15 10 5 1. 86682 1. 82236 1 77760 1. 73021 25.327. 6 3o. 6 34. 0

F139 F138 F95 F F49 F35 F152 F140 F141 F142 F143 F144 N 0te.Liquidustemperatures above 1300 C.

Lego; SERIES F40 F52 F111 F123 F53 F F63 S10 50 50 50 50 50 50 50 B11030 26 24 23 22 20 1S T101 20 20 20 20 20 20 20 143303- 4 6 7 8 1O 12'Liq. temp., degrees 1, 320 1, 275 1, 253 1, 235 1, 257 1, 315 1, 315

See footnotes at end of table.

Table Ill-Continued Z103 SERIES F123 F124 F125 F130' F126 F127 F128 S10:48 46 45 44 42 40 1215.0" 7 23 23 23 23 23 1101 20 20 20 20 20 20 L250;7 7 7 7 7 7 z; 2 4 0 s Llq. temp., degrees 1, 235 1, 230 1, 217 1, 2151, 227 1, 302 N 1. 79570 1. 80760 1. 81928 1. 82531 1. 83157 1. 8430434. 2 33. 8 33. 4 33. 2 33. 0 32.6

T210 SERIES F135 F136 F137 Th0; SERIES TABLE Iv [Compositions in molepercent] F153 F154 F155 F158 Lam, SERIES 45 45 45 44 21 17 1 19 F138F189 F190 F191 2? 2; 20 2g 1, 218 1, 227 1, 310 1 83251 1. 84051 1.847081 83034 1 $331 1 331 33.0 32.9 334 .2 I 2&5 I 2 7 F201 F192 F193 F194PbO-WO; SERIES 40 40 1 22 20 18 F159 F160 F161 7 F162 g 1 173 1 44' 4a42' 20 19 1s 17 20 20 20 20 7 7 7 7 5 5 s is 3 a a a ZrOa SERIES 1 2 a 12- 3 1.84905 1.86040 1.87384 F201 F198 F216 F199 F208 F200 '40 3s 37 as35 31 23 f 23 2e 23 23 23 Opal in center; trans. sample only. 30 30 3030 30 30 *Devitinmold. 7 7 7 7 7 7 I Contained crystals. ZI 2 3 4 5 6Liq. temp, c 1,242 1,238 1,212 1, 250 1, 279 ND 1.87393 1.8861 1.8901 1.89748 1.9028 1. 90812 7 23.7 V 28.4 28.3 28.2 28.1 28.0 Glass F40,containing in mole percent, SiO -SO, BaO-30, and TiO -20,-was chosen asthe base glass Tho SERIES for further substitutions for the series shownin Table 1 III. This table includes the La O series, the Zr0 series, theThO series, and the PbO-WO series. In the F216 F217 F218 F219 La 0series transmittances of 71.5 percent were obtmned 37 37 37 on 2 mm.thick samples in the range of 3 to 4.1 microns. 23 21 19 17 This is anoutstandingly high value of transmittance. 35 3( 32 3( As shown in TableIV, below, a series of glasses have 3 3 3 been made based on the ternaryglass F138, which con- 1 2 +9. 15263 1 3 1 358 tains in mole percent,810 -40, BaO-30, no -30. f The oxides substituted in the series are La oZrO -2 ,28-2 28.1

Th0}, and T3305.

T210 SERIE S FIG. 4 shows the eifect on N and Nu for the substitution ofLa for BaO in glass F138. The substitution gives the unusual result ofincreasing the refractive index and, at the same time, increasing the Nuvalue. This is a significant result when it is considered that mostsubstitutions that cause an increase in refractive index normallyproduce a decrease in Nu value.

The transmittance of 2 mm. thickness of glasses in the La 0 series aregiven in FIGS. and 6. The transmittance in the 3.0 to 4.25 micron wavelength region generally increases as the La O content of the glasses isincreased.

In the ZrO series, shown plotted in FIG. 7, the transmittances varysomewhat with composition, but all of them remain between 65 and 70%from 3.0 to 4.25 microns. Transmittances for glasses F217 and F218 inthe Th0 series are plotted in FIG. 8.

In the T110 series, T110 was substituted for BaO; and in the Ta Oseries, Ta O was substituted for SiO The refractive index, N increasesfaster for the Ta O substitution than for the T110 substitution;however, it has been found that the liquidus temperature increases veryrapidly with the Ta O substitution and for practical purposes one molepercent of Ta O is about the limit that can be used.

The compositions, liquidus temperatures, refractive indices, N and Nuvalues of glasses which are variations of the Ta O and ThO series listedin Table IV are given in the following table:

TABLE V [Compositions in mole percent] F220 F223 F224 F231 Lin. Temp., C1,260 l, 253 l, 320

F232 F233 F234 F235 It is important to note that all of the glasses haverefractive indices, N above 1.90, and as such are comparable to therefractive index of a high PbO content glass A2059. The deformationtemperature of both glasses F223 and F232 is above 800 C. as compared to425 C. for glass A2059.

Two glasses of the invention, F234 and F235 of Table V, are germanateglasses. The only difference between the germanate glasses and glassesF223 and F232 of Table II is that SiO has been completely replaced withGeO The refractive indices, N are appreciably higher than for thesilicate glasses. The transmittance of 2 mm. thicknesses of F223 andF234 and similar data for F232 and F235 are shown in FIGS. 9 and 10,respectively. Due to the high cost of 6e0 about $150.00 a pound at thepresent time, large melts of F234 and F235 have not been attempted.However, based on the experiences with F223 and F232, it is believedthat these glasses could be made in at least 6000 gram melts withoutdevitrification troubles. More specifically, the glasses F223 and F232have been produced in 6000 gram melts and cooled without devitrificationinto slabs of relatively large dimensions; i.e., 12" x 6 /2" x 2". Also,it has been found by this invention that other glass compositions, suchas multicomponent glasses F158 and F161 of Table III above which weredeveloped from the ternary base glasses, can be made successfully in6000 gram melts and cooled without devitrification. These glasses alsohave the desirable properties of the glasses hereinbefore mentioned.

The transmittance of 2 and 8 mm. thicknesses and the calculatedabsorbance indices for F158 and F161 are given in FIGS. 11 and 12,respectively, and the linear thermal expansion curves for the twoglasses are given in FIGS. 13 and 14.

It has been found that glasses of the BaOTiO -SiO type have high valuesof elastic moduli as compared to standard types of glasses. For example,the room temperature values of F 158 and F 161 and their comparison withsome well-known glasses are as follows:

The values for F158 and F161 for elevated temperatures are plotted inFIG. 15. The shape of the curves are similar to those for most types ofglasses; i.e., the temperature coetficients of elastic moduli isnegative. In comparison, fused silica and Corning 7740, a Pyrex typeglass, have positive temperature coefiicients of elastic moduli up tothe annealing range. The values obtained on glasses F 15 8 and F 161 arehigher than those of most glasses with only the calcium aluminateglasses having comparable values.

This invention provides glasses containing BaO, TiO and SiO as theprincipal constituents, and series of glasses based on this ternarysystem. By way of example, this specification has described series basedon glasses having a mole percent composition of SiO -50, BaO30, TiO 20;and SiO 40, BaO30, and TiO -30.

Variations of two of the members of the series, Ta O and ThO based onthe latter mole percent composition expressed in the preceding paragraphare also presented as examples of the many glasses which may be formedin the light of the teachings of the invention. These glasses also havedesirable characteristics such as high refractive indices, goodtransmittances in the near infrared at Wave lengths below five microns,high deformation temperatures, good chemical durabilities, and thecapability of being formed in large amount melts.

The glasses of the instant invention are useful where infraredtransmitting glasses are required as in fire control and other opticaldevices, for making achromatically corrected lens systems which needglasses having high refractive indices and dispersions over aconsiderable range,

1. A NON-CRYSTALLINE INFRARED TRANSMITTING GLASS HAVING A MELTING POINTOF LESS THAN 2750*F., AND HIGH REFRACTIVE INDEX, HIGH DEFORMATIONTEMPERATURES, GOOD RESISTANCE TO